Effects of Both Inherent Chemical Structure and Environment Conditions on the Enzyme-Small Molecule Relationship of a Non-Oxime Reactivator of Organophosphorus-Inhibited Human Acetylcholinesterase.

Organophosphorus (OP) nerve agents and pesticides inhibit the enzyme acetylcholinesterase (AChE) via a covalent interaction at the active site, resulting in a buildup of excess acetylcholine in the synaptic cleft. Current reactivators rely exclusively on oxime moieties that can reverse this inhibition via direct nucleophilic attack of the bound OP at the enzyme active site. Absolute molar concentration is a fundamental component of the mechanism of oxime-mediated reactivation and forms the basis of established reactivation kinetics theory and descriptive mathematics. Recently, a non-oxime reactivator (ADOC) was discovered that operates via a general acid-base catalysis mechanism, which calls the fundamental assumptions of established reactivation kinetics theory into question. The objective of this study is to determine if the assumption that reactivation occurs in an absolute concentration-dependent manner holds true for ADOC. An assay was developed to elucidate the effect of reactivator and enzyme concentration relationships as a component of either inherent compound structure-activity or external environment-activity relationships, and this was utilized to evaluate both an oxime and non-oxime reactivator. Initial results suggest that while chemical structure and, therefore, mechanism of reactivation play a role in the reactivator-to-enzyme interaction, environmental factors are suspected to also impact this relationship only for ADOC, likely via activation of an alternate reactivation mechanism. In conclusion, expanding the reactivation kinetics theory to accommodate alternate mechanisms of reactivation may pave new avenues for the development of nerve agent countermeasure therapeutics.